The link between cyclic adenylic acid and activation of CO2 fixation in hepatic mitochondria will continue to be sought. Search will be made for conditions that will permit satisfactory maintenance of CO2 fixation in incubated mitochondria. Under these conditions the mitochondria can be used to test potential stimulating substances that may be evoked in livers treated with adenylic acid. Studies designed to elucidate the nature of the changes in the mitochondria caused by cyclic adenylic acid will continue. These will include electron microscopy as well as metabolic studies of urea and ketone body formation.